Chealators of type XN1 S1 X1 for radioactive isotopes, their metal complexes and their diagnostic and therapeutical uses

ABSTRACT

This invention relates to new bifunctional chelating agents with intermittent chalcogen atoms, pharmaceuticals containing these compounds, their use in radiodiagnostics and radiotherapy, and methods for the production of these compounds. 
     The compound according to the invention has the general formula (I) 
     
         M--L 
    
     where M represents a radionuclide and L a ligand of the general formula (II). 
     It was found, surprisingly, that these new, bifunctional chelating agents with intermittent chalcogen atoms and their coupling products with compounds that accumulate specifically are excellently suited for producing radiopharmaceuticals for diagnostic and therapeutic purposes.

This application is a 371 of PCT/DE94/00372 Mar. 29, 1994.

TECHNICAL FIELD OF THE INVENTION

This invention relates to new bifunctional chelating agents with intermittent chalcogen atoms, pharmaceuticals containing these compounds, their use in radiodiagnostics and radiotherapy, and methods for the production of these compounds.

BACKGROUND OF THE INVENTION

It has been known for a long time that complexing agents for radioactive isotopes or their complexes with radioactive metals can be applied in radiodiagnostics and radiotherapy. Technetium-99m is the most frequently used radionuclide in radiodiagnostics because it is particularly well suited for in-vivo applications due to its favourable physical properties (no corpuscular radiation, low half-life of 6.02 h, good detectability by 140 keV γ-radiation) as well as its low biological half-life and easy availability. The first step of forming complexes of technetium-99m is to gain pertechnetate from a nuclide generator; it is then converted to a lower oxidation number using appropriate reductants (such as SnCl₂, S₂ O₄ ²⁻, etc.). This oxidation number is stabilized by an appropriate chelating agent. As technetium may have several oxidation numbers (+7 to -1) which may vehemently alter its pharmacological properties by changing the charge of the complex, it is necessary to provide chelating agents or complex ligands for technetium-99m that are capable of binding technetium in a specific oxidation number safely, firmly and stably to prevent undesirable biodistribution due to in-vivo redox processes or release of technetium from the radiodiagnostic agent which would impede the safe diagnosis of the respective diseases.

For example, cyclic amines (Troutner, D. E. et al.: J. Nucl. Med. 21, 443 (1980)) are regarded as suitable complexing agents for technetium and rhenium isotopes but their disadvantage is that they are only capable of binding technetium-99m in sufficient quantities from a pH value >9. N₂ O₂ systems (Pillai, M. R. A., Troutner, D. E. et al.: Inorg. Chem., 29, 1850 (1990)) are in clinical use. Non-cyclic N₄ systems such as HMPAO have the great disadvantage of low complex stability. Tc-99m-HMPAO has to be applied immediately after labelling due to its low stability (Ballinger, J. R. et al., Appl. Radiat. Isot. 42, 315 (1991); Billinghurst, M. W. et al., Appl. Radiat. Isot. 42, 607 (1991)) to keep the portion of decomposition products low which have different pharmacokinetic and excretion properties. Such radiochemical impurities make detection of the diseases to be diagnosed more difficult. Any coupling of these chelates or chelating agents with other substances that accumulate selectively in centres of diseases cannot be broken by simple means so that these normally spread unspecifically in the organism.

N₂ S₂ chelating agents (Bormans, G. et al.: Nucl. Med. Biol., 17, 499 (1990)) such as ethylene dicysteine (EC; Verbruggen, A. M. et al.; J. Nucl. Med. 33, 551 (1992)) meet the requirement of sufficient stability of their respective technetium-99m complex but form radiodiagnostic agents of a purity greater than 69% only at pH values >9. N₃ S systems (Fritzburg, A.; EPA 0 173 424 and EPA 0 250 013) yield stable technetium-99m complexes but have to be heated up to temperatures of ca. 100° C. to insert the radionuclide. Another disadvantage of N₂ S₂ and N₃ S systems is that they are discharged too rapidly and without specific accumulation in the organism. Thus they are only used clinically, though to a limited extent, in renal function diagnostics. Their use is limited mainly because the demand has increased for substances that accumulate specifically in diseased tissues. This can be accomplished if one manages to link complexing agents easily with selectively accumulating substances while the latter retain their favourable complexing properties. But as it happens quite frequently that a certain reduction of complex stability can be observed after coupling the complexing agent to such a molecule by means of one of its functional groups, previous approaches to coupling chelating agents with substances that accumulate selectively are hardly satisfactory because a quantity of the isotope that is not tolerable with a view to diagnostics is released in vivo from the conjugate (Brechbiel, M. W. et al.; Inorg. Chem. 1986, 25, 2772). It is therefore necessary to produce bifunctional complexing agents that have functional groups to bind the desired metallic ion and one (or several other) functional groups to bind the selectively accumulating molecule. Such bifunctional ligands allow specific, chemically defined bonding of technetium or rhenium isotopes to the most various biological materials even in cases in which pre-labelling is applied. Some chelating agents coupled with monoclonal antibodies (e.g. EP Appl. 0 247 866 and EP Appl. 0 188 256) or fatty acids (EP Appl. 0 200 492) have been described. But these were based on the N₂ S₂ systems mentioned above which are hardly appropriate due to their low stability. As both the properties of the substances that accumulate selectively and the mechanisms of accumulation are quite varied, one should be able to vary the chelating agent meant for coupling to adapt it to the physiological requirements of its partner with regard to lipophilic or hydrophilic behaviour, membrane permeability or impermeability, etc.

SUMMARY OF THE INVENTION

It is therefore a problem of this invention to provide stable complex compounds coupled with or capable of coupling with various compounds that accumulate selectively, and to provide such chelating agents or complexes whose substituents show a wider range of chemical variation to be adaptable to the above requirements. It is another problem of this invention to provide such compounds and pharmaceuticals containing these compounds, as well as methods for their production.

This problem is solved by the invention, surprisingly, in that the new, uncommon, bifunctional chelating agents with intermittent chalcogen atoms and their coupling products with compounds that accumulate selectively are excellently suited for producing radiodiagnostic and radiotherapeutic agents.

BRIEF DESCRIPTION OF THE DRAWINGS

The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawing(s) will be provided by the Patent and Trademark Office upon request and payment of the necessary fee.

FIG. 1 illustrates a Sudan-III-staining and an autoradiography of the aorta of a WHHL-rabbit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The object of this invention are compounds of the general formula (I)

    M--L                                                       (I)

wherein

M represents a radionuclide of Tc or Re and L represents a ligand of the general formula (II)

    B--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (II)

wherein

A,A' are same or different and represent an O, S, or Se chalcogen atom,

R¹, R², R³, R⁴, R⁵, and R⁶ are same or different and represent a hydrogen atom and/or a branched or unbranched C_(l) -C₆ alkyl residue,

B represents a residue

    --NH--(CR.sup.7 R.sup.8)--(CR.sup.9 R.sup.10).sub.n=1,2 --S--R.sup.11,

wherein

R⁷ and R⁸ are same or different and represent a hydrogen atom or an unbranched, branched, cyclic, or polycyclic C₁ -C₆₀ alkyl, alkenyl, polyalkenyl, alkinyl, polyalkinyl, aryl, alkylaryl, or arylalkyl residue which may optionally be replaced by carboxy, aminocarbonyl, alkoxycarbonyl, amino, aldehyde, hydroxy, oxo, oxy, or alkoxy groups containing up to 20 carbon atoms, and may optionally be interrupted, or replaced, by one or several heteroatoms from the series of O, N, S, P, As, Se,

R⁹ and R¹⁰ are same or different and represent a hydrogen atom and/or a branched or unbranched C₁ -C₆ alkyl residue, R¹¹ represents a hydrogen atom, a sulfur protective group, or residues like R⁷ or R⁸,

with R⁷ and R¹¹, together with the groups that connect them, optionally forming a 4- to 8-membered ring which may optionally be replaced by hydroxy, oxo, oxy, or alkoxy groups containing up to 6 carbon atoms,

R¹² represents a hydrogen atom or chalcogen protective group.

Preferred compounds of the general formula (I) are characterized in that A and A' are sulfur atoms, and that R¹² represents a hydrogen atom or a sulfur protective group.

Particularly preferred compounds of the general formula (I) are in addition characterized in that R⁷ and R⁸ are different, and R⁸, R⁹ and R¹⁰ each represent a hydrogen atom.

Another object of this invention is related to the new, bifunctional ligands with intermittent chalcogen atoms of the general formula (II).

    B--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (II)

wherein R¹, R², R³, R⁴, R⁵, R⁶, A, A', and B have the meaning specified above.

Preferred compounds according to the invention of the general formula (II) are characterized in that A and A' are sulfur atoms, and that R¹² represents a hydrogen atom or a sulfur protective group.

Particularly preferred compounds according to the invention of the general formula (II) are in addition characterized in that R⁷ and R⁸ are different, and R⁸, R⁹ and R¹⁰ each represent a hydrogen atom.

Yet another object of this invention are conjugates containing compounds of the general formulae (I) and/or (II) and substances that accumulate selectively in diseased tissues, with a covalent bond existing between these substances, said bond being amidic if the substances are amino groups such as peptides, proteins, antibodies, or their fragments, ester-like if the substances contain hydroxy groups, and imidic if the substances contain aldehyde groups.

Particularly preferred conjugates according to the invention are characterized in that the substances that accumulate in diseased tissue are peptides such as endothelines, partial endotheline sequences, endotheline analogues, endotheline derivatives, or endotheline antagonists.

Other preferred embodiments of the conjugates according to the invention are characterized in that the peptides comprise the following sequences or parts thereof: ##STR1##

The compounds according to the invention of the general formula (I) are produced by reacting technetium-99m in the form of pertechnetate or Re in the form of perrhenate in the presence of a reductant and, optionally, an auxiliary ligand, with a compound of the general formula (II)

    B--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (II)

wherein R¹, R², R³, R⁴, R⁵, R⁶, A, A', and B have the meaning specified above.

The ligands according to the invention of the general formula (II) are produced by reacting compounds of the general formula (III) with compounds of the general formula (IV) according to the following reaction scheme:

    X--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (III)

    +NH.sub.2 --(CR.sup.7 R.sup.8)--(CR.sup.9 R.sup.10).sub.n=1,2 --S--R.sup.11(IV)

    →X--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (II)

wherein

X is a leaving group and R¹, R², R³, R⁴, R⁵, R⁶, A, A', and B have the meaning specified above.

These reactions are carried out in polar and non-polar aprotic solvents such as dichloromethane, tetrahydrofurane, chloroform, 1,4-dioxane, DMF, or DMSO at temperatures between -30 and +100° C.; an auxiliary base is added to trap any acids that may be liberated. Among these bases could be, for example: tertiary amines, alkali and alkaline-earth hydroxides, alkali and alkaline-earth carbonates.

Another object of the present invention is a kit for producing radiopharmaceuticals consisting of a compound of the general formula (II) or a conjugate according to the invention containing compounds of the general formulae (I and/or II) and substances that accumulate selectively in tissues, a reductant and, optionally, an auxiliary ligand, said agents being either dry or in solution, instructions for use including instructions for reacting the compounds described with technetium-99m or rhenium in the form of a pertechnetate or perrhenate solution.

Another object of this invention is a radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques. It contains a compound of the general formula (I) or a conjugate according to the invention containing compounds of the general formulae (I and/or II) and substances that accumulate selectively in tissues, optionally with the adjuvants common in galenics, and that the compound is prepared in a kit using technetium-99m or rhenium in the form of a pertechnetate or perrhenate solution.

Yet another object of this invention is a method for carrying out radiodiagnostic examinations according to which the radiopharmaceutical formulation is applied at doses from 0.5 mCi to 10 mCi per 70 kg of a patient's body weight and radiation emitted by the patient is recorded.

Many of the synthesized chelates that were labelled with Tc-99m or Re surprisingly showed a greater stability than comparable N₂ S₂ and N₃ S systems described in the literature. For example, no decomposition products were found of a substance according to the invention (Examples 3a, 3b) coupled with a fatty alcohol even after 26 hours. It was also found in competition tests that the Tc-99m or Re chelating agents complex better than comparable N₂ S₂, N₃ S and propylene aminoxinum systems. The chelates and chelating agents described in the present invention are clearly better suited for diagnostic and therapeutic purposes than the systems known so far. It is a specific advantage of the chelating agents according to the invention that they may be synthesized without sulfur protective groups. This makes synthesis very simple; in addition, the compounds described according to the invention, when radiolabelled, do not contain any other foreign molecules in the solutions used for radiodiagnostics or radiotherapy, for example, solutions to be administered intravenously. Biodistribution of the radiopharmaceutical and thus the value of diagnostic information are frequently diminished by such foreign molecules. Moreover, such ligands or their coupling products with substances that accumulate selectively in diseased tissues can be labelled very gently. The ligands according to the invention sud their coupling products with substances that accumulate selectively in diseased tissues can be labelled at room temperature and at the physiological pH value without having to split off protective groups using bases, acids, or other auxiliary substances known to a person skilled in the art. This guarantees that the very sensitive substances that accumulate selectively in diseased tissues are not altered chemically by such auxiliary substances, which frequently reduces selective accumulation in diseased tissue and diminishes the value of radiodiagnostic information.

Sulfur protective groups may be used here, of course, if the disadvantages described can be accepted. The groups are attached to sulfur atoms and split off according to methods known to a person skilled in the art. The ways in which the substances that accumulate selectively in diseased tissues are bonded are also known to a person skilled in the art (e.g. Fritzberg et al.; J. Nucl. Med. 26, 7 (1987)), for example, by a reaction of electrophilic groups of the complex ligand with nucleophilic centres of the substances that accumulate selectively in diseased tissues. Otherwise, nucleophilic groups of the chelating agent are coupled with electrophilic groups of the substances that accumulate selectively in diseased tissues.

The partners for coupling are, among others, various biomolecules, ligands that bond to specific receptors which are capable of detecting tissue showing a modified receptor density. This includes peptides, steroid hormones, growth factors, neurotransmitters. Ways for improved diagnosis of carcinomas of the breast and the prostata were shown using ligands for steroid hormone receptors (S. J. Brandes and J. A. Katzenellenbogen, Nucl. Med. Biol. 15, 53, 1988).

Tumour cells sometimes show a modified density of receptors for peptide hormones or growth factors such as the epidermal growth factor (EGF). The differences in concentration could be utilized for selective accumulation of cytostatic agents in tumour cells (E. Aboud-Pirak et al., Proc. Natl. Acad. Sci. USA 86; 3778, 1989). Ligands for neuroreceptors labelled with positron-emitting isotopes were successfully used for the diagnosis of various brain diseases (J. J. Forst, Trends in Pharmacol. Sci., 7, 490, 1989). Other biomolecules are metabolites that can be introduced into the metabolism to make changes visible; this includes fatty acids, saccharides, peptides, and amino acids. Fatty acids that were coupled with the more unstable N₂ S₂ chelating agents have been described in EPA 0 200 492. Other metabolic products such as saccharides (desoxyglucose), lactate, pyruvate, and amino acids (leucine, methylmethionine, glycine) were used in the PET technique for visualizing changes in metabolic processes (R. Weinreich, Swiss Med., 8, 10, 1986). Likewise, non-biological substances such as misonidazol and its derivatives which bond irreversibly to cell components in tissues or parts of tissues with a reduced oxygen concentration, can be used for specific accumulation of radioactive isotopes and thus for the visualization of tumours or ischaemic regions (M. E. Shelton, J. Nucl. Med. 30; 351, 1989). Eventually, bifunctional chelating agents may be coupled with monoclonal antibodies or their fragments. Coupling products of the chelating agents according to the invention or their technetium-99m or Re complexes with fatty alcohols, fatty alcohol derivatives, or fatty amines and their derivatives, or with endothelines, partial endotheline sequences, endotheline analogues, endotheline derivatives, or endotheline antagonists have proved particularly favourable for the detection of atherosclerotic vascular diseases. These derivatives were applied to WHHL rabbits that had high LDL concentrations in their blood--and thus atherosclerotic lesions--due to a genetic defect of their LDL receptor. Concentration quotients from 3 to 40 were found in atheromatose plaques as compared with undamaged tissue about 4 to 5 hours after i.v. application of the derivatives to WHHL rabbits. This allowed to detect atherosclerotic areas of vessels using the common methods of radiodiagnostics (e.g. a gamma scintillation camera). Only very late stages of atherogenesis could up to now be diagnosed by using more invasive methods (e.g. arteriography). The substances according to the invention provide the decisive advantage of being able to diagnose much earlier stages of atherosclerosis using less invasive methods.

It is unimportant whether the chelating agent is labelled with Tc-99m or Re before or after coupling with the selectively accumulating molecule. But if coupling takes place after complexing, the condition is that the reaction of the radioactive complex with the accumulating compound is rapid, gentle, and nearly quantitative, requiring no subsequent purification.

The radiopharmaceuticals of the invention are produced in a generally known way by dissolving the complexing agents according to the invention in an aqueous medium and adding a reductant, preferably tin(II) salts such as chloride or tartrate, optionally adding the adjuvants common in galenics, and subsequent sterile filtration. Among the suitable additives are physiologically tolerable buffers (such as tromethamine), small quantities of electrolytes (e.g. sodium chloride) or stabilizers (e.g. gluconate, phosphate, or phosphonate). The pharmaceutical according to the invention is either available as a solution or as lyophilizate and is mixed shortly before application with a solution of Tc-99m pertechnetate, eluated from commercial generators, or a perrhenate solution.

For in-vivo applications in nuclear medicine, the agents according to the invention are administered at doses from 1×10⁻⁵ to 5×10⁴ mol/kg of body weight. The amount of radioactivity, based on an average body weight of 70 kg, is between 0.05 and 50 mCi, preferably between 5 and 30 mCi, for diagnostic applications. For therapeutic applications, doses applied are between 5 and 500 mCi, preferably 10 to 350 mCi. Normally, 0.1 to 2 ml of a solution of the agents according to the invention is applied by intravenous, intra-arterial, peritoneal or intra-tumoral injection. The intravenous injection is preferred.

The following examples shall explain the object of this invention in greater detail.

EXAMPLE 1a 2,5-dithia cyclohexanone

48 ml (0.6 mol) of chloroacetyl chloride dissolved in 300 ml of anhydrous dichloromethane are added by dropping to an agitated and ice-cooled solution of 51 ml (0.6 mol) of 1,2-dimercapto ethane and 168.0 (1.2 mol) of triethyl amine in 600 ml of anhydrous dichloromethane. Afterwards, the mixture is stirred at room temperature for 3 hours. The triethyl amine hydrochloride is filtered off, and the organic phase is washed with water. After drying above magnesium sulfate, the solvent is evaporated under reduced pressure, and the residue distilled in vacuo. (Following J. Larsen et al., Synthesis, 1989, 134).

Yield: 52 g (65%), yellowish oil

    ______________________________________     Analysis:     ______________________________________     Calc.: C 35.80                 H 4.51      O 11.92 S 47.76     Found: C 35.63                 H 4.68              S 47.49     ______________________________________

EXAMPLE 1b S-(2-mercaptoethyl)-N-(2-mercapto-1-(methoxycarbonyl)-ethyl)-mercaptoacetamide

13.42 g (0.1 mol) of 2,5-dithia hexanone dissolved in 250 ml of anhydrous dichloromethane are added by dropping, and in an argon atmosphere, to a solution of 17.16 g (0.1 mol) of cysteine methyl ester hydrochloride and 10.12 g (0.1 mol) of triethyl amine in 500 ml of anhydrous dichloromethane. The reaction mixture is kept agitated overnight at room temperature and then washed three times with 2% aqueous citric acid, saturated sodium hydrogen-carbonate solution and with water. After drying above sodium sulfate, the solvent is evaporated under reduced pressure. The oily residue is crystallized by trituration with diethyl ether.

Yield: 21.32 g (79.1%), white powder

    ______________________________________     Analysis:     ______________________________________     Calc.: C 35.67                 H 5.61  N 5.20    O 17.82                                         S 35.70     Found: C 35.48                 H 5.72  N 4.97          S 35.43     ______________________________________

EXAMPLE 1c S-(2-mercaptoethyl)-N-(2-mercapto-1-(methoxycarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 1b are dissolved in 1.0 ml of 0.5 M phosphate buffer, pH 7.5. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 7.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml), 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >98%.

EXAMPLE 2a S-(2-mercaptoethyl)-N-(2-mercapto-1-(hydroxycarbonyl)-ethyl)-mercaptoacetamide

2.69 g (10 mmol) of the ligand produced according to Example 1b are dissolved in 200 ml of 2N aqueous sodium hydroxide solution in an argon atmosphere. After 2 hours of stirring at room temperature, the solution is set using argon-saturated concentrated hydrochloric acid, pH=3; the sedimented oily residue is exhaustively extracted with acetic ester. After drying above sodium sulfate, the solvent is evaporated under reduced pressure. The oily residue is crystallized by trituration with diethyl ether.

Yield: 732 mg (28.7%), white powder

    ______________________________________     Analysis:     ______________________________________     Calc.: C 32.92                 H 5.13  N 5.49    O 18.80                                         S 37.66     Found: C 32.73                 H 5.38  N 5.30          S 37.41     ______________________________________

EXAMPLE 2b S-(2-mercaptoethyl)-N-(2-mercapto-1-(hydroxycarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 2a are dissolved in 1.0 ml of 0.5 M phosphate buffer, pH 7.5. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 7.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml), 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >98%.

EXAMPLE 3a S-(2-mercaptoethyl)-N-(2-mercapto-1(decyloxycarbonyl)-ethyl)-mercaptoacetamide

13.42 g (0.1 mol) of 2,5-dithia cyclohexanone dissolved in 250 ml of anhydrous dichloromethane are added by dropping, and in an argon atmosphere, to a solution of 29.79 g (0.1 mol) of cysteine decyl ester hydrochloride and 10.12 g (0.1 mol) of triethyl amine in 500 ml of anhydrous dichloromethane. The reaction mixture is kept agitated overnight at room temperature and then washed three times with 2% aqueous citric acid, saturated sodium hydrogencarbonate solution and with water. After drying above sodium sulfate, the solvent is evaporated under reduced pressure. The oily residue is crystallized by trituration with diethyl ether.

Yield: 31.45 g (79.5%), white powder

    ______________________________________     Analysis:     ______________________________________     Calc.: C 51.61                 H 8.41  N 3.54    O 12.13                                         S 24.31     Found: C 51.48                 H 8.52  N 3.40          S 24.05     ______________________________________

EXAMPLE 3b S-(2-mercaptoethyl)-N-(2-mercapto-1-(decyloxycarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 3a are dissolved in 1.0 ml of ethanol. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 8.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml), 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >95%.

EXAMPLE 4a S-(2-mercaptoethyl)-N-(2-mercapto-1-(2-methoxyethoxycarbonyl)-ethyl)-mercaptoacetamide

2.69 mg (10 mmol) of the ligand described in Example 1b are refluxed in an argon atmosphere for 6 hours in 250 ml of anhydrous ethylene glycol monomethyl ether in the presence of 190 mg (1 mmol) of toluene-p-sulfonic acid hydrate. Then the solvent is evaporated under reduced pressure and the oily residue is taken up in dichloromethane. The dichloromethane solution is washed three times with 2% aqueous citric acid, saturated sodium hydrogencarbonate solution and with water. After drying above sodium sulfate, the solvent is evaporated under reduced pressure. The obtained oil is chromatographed on silica gel (eluent: dichloromethane/methanol 8:2). Finally, it is recrystallized from diethyl ether.

Yield: 632 mg (22.2%), white powder

    ______________________________________     Analysis:     ______________________________________     Calc.: C 38.32                 H 6.11  N 4.47    O 20.42                                         S 30.68     Found: C 38.14                 H 6.37  N 4.18          S 30.41     ______________________________________

EXAMPLE 4b S-(2-mercaptoethyl)-N-(2-mercapto-1-(2-methoxyethoxycarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 4a are dissolved in 1.0 ml of ethanol. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 8.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml), 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >95%.

EXAMPLE 5a S-(2-mercaptoethyl)-N-(2-mercapto-1-(octylaminocarbonyl)-ethyl)-mercaptoacetamide

70 ml of n-octylamine are added to a solution of 2.69 g (10 mmol) of the ligand produced according to Example 1b in 30 ml of ethanol; the reaction mixture is then heated to boiling for 6 h in an argon atmosphere. It is evaporated in a medium high vacuum, and the residue is mixed in an argon atmosphere with 200 ml of 2% aqueous citric acid and 200 ml of dichloromethane. The mixture is strongly agitated for 15 minutes, the dichloromethane phase is separated and washed three times with 2% aqueous citric acid, saturated sodium hydrogencarbonate solution and with water. After drying above sodium sulfate, the solvent is evaporated under reduced pressure. The residue is chromatographed on silica gel (eluent: dichloromethane/methanol 95:5). Finally, it is recrystallized from diethyl ether.

Yield: 548 mg (14.9%), white powder

    ______________________________________     Analysis:     ______________________________________     Calc.: C 49.15                 H 8.25  N 7.64    O 8.73                                         S 26.24     Found: C 49.08                 H 8.31  N 7.66          S 26.02     ______________________________________

EXAMPLE 5b S-(2-mercaptoethyl)-N-(2-mercapto-1-(octylaminocarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 5a are dissolved in 1.0 ml of ethanol. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 8.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml), 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >95%.

EXAMPLE 6a S-(2-mercaptoethyl)-N-(2-mercapto-1-(2,3-dihydroxypropylaminocarbonyl)-ethyl)-mercaptoacetamide

2.69 g (10 mmol) of the ligand produced according to Example 1b are dissolved in 30 ml of ethanol and 30 ml of aminopropandiol and heated to boiling for 7 hours in an argon atmosphere. The ethanol is distilled off under reduced pressure, and the residue is mixed with argon-saturated water; a pH value of 7 is set using argon-saturated concentrated hydrochloric acid. The yellowish solution is lyophilized and the residue chromatographed on silica gel RP 18 (eluent: water, tetrahydrofurane 0-50%). A colourless glass is obtained after evaporating the solvent.

Yield: 378 mg (10%), colourless glass

    ______________________________________     Analysis related to the anhydrous substance:     ______________________________________     Calc.: C 36.57                 H 6.14  N 8.53    O 19.48                                         S 29.28     Found: C 36.31                 H 6.47  N 8.34          S 29.01     ______________________________________

EXAMPLE 6b S-(2-mercaptoethyl)-N-(2-mercapto-1-(2,3-dihydroxypropylaminocarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 6a are dissolved in 1.0 ml of ethanol. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 8.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml); 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >95%.

EXAMPLE 7a S-(2-mercaptoethyl)-N-(2-mercapto-1-(carbonyl-his-leu-asp-ile-ile-trp)-ethyl)-mercaptoacetamide

134 mg (1 mmol) of 2,5-diethyl cyclohexanone (Example 1a) are added in an argon atmosphere to a solution of 900 mg (1 mmol) of NH₂ -cys-his-leu-asp-ile-ile-trp SEQ ID NO: 15 (produced in a similar way as described by Barany and Merrifield, The Peptides: Analysis, Biology, Academic Press, New York 1980; Stewart and Young, Solid Phase Peptides Syntheses, 2nd ed., Pierce Chemical W., Rockford, II, 1984) and 304 mg (3 mmol) of triethyl amine in 100 ml of dimethyl formamide. The reaction mixture is stirred at room temperature for 13 hours. When the reaction is finished, the solution is filtered and the solvent removed under reduced pressure. The residual oil is mixed three times with 50 ml of dimethyl formamide and evaporated each time. The residue is stirred up with 100 ml of anhydrous diethyl ether. A white solid material settles down which is filtered off. The material is recrystallized from mixtures of dimethyl formamide and diethyl ether for purification.

Yield: 423 mg (40.9%), white powder

    ______________________________________     Analysis related to the anhydrous substance:     ______________________________________     Calc.: C 53.47                 H 6.63  N 13.56   O 17.03                                         S 9.31     Found: C 53.19                 H 6.92  N 13.28         S 8.97     ______________________________________

EXAMPLE 7 S-(2-mercaptoethyl)-N-(2-mercapto-1-(carbonyl-his-leu-asp-ile-ile-trp)-ethyl)-mercaptoacetamide, technetium-99m complex

10 mg of the ligand produced according to Example 7a are dissolved in 1.0 ml of ethanol. 50 μl of this ligand solution are mixed with 250 μl of phosphate buffer, pH 8.5, 50 μl of a deoxygenated aqueous citrate solution (50 mg/ml), 2.5 μl of a deoxygenated aqueous tin(II) chloride solution (5 mg/ml 0.05 N HCl), and 100 μl of a pertechnetate solution (400-900 μCi). After an incubation time of 10 minutes, the reaction mixture is tested for purity of the Tc complex formed using HPLC: Hamilton PRP-1 column, 5 μm, 125×4.6 mm; gradient eluation from 100% A to 100% B within 7.5 minutes (eluent A: sodium hydrogenphosphate, 0.005 M, pH 7.4; eluent B: acetonitrile/sodium hydrogenphosphate, 0.005 M, pH 7.4 (75/25); 2.0 ml/min. Radiochemical purity is >95%.

EXAMPLE 8 Accumulation of S-(2-mercaptoethyl)-N-(2-mercapto-1-(decyloxycarbonyl)-ethyl)-mercaptoacetamide, technetium-99m complex, in atherosclerotic vascular lesions of WHHL rabbits

S-(2-mercaptoethyl)-N-(2-mercapto-1-(decyloxycarbonyl)-ethyl)-mercaptoacetamide (produced according to Example 3a) is labelled as described in Example 3b.

99.9 GBq (2.7 mCi) of the substance labelled according to Example 3b were diluted to 1 ml with phosphor-buffered saline and administered via the ear vein to a narcotized WHHL rabbit, Rompun/Ketavet (1:2). The rabbit was killed 5 hours after the application, and an autoradiogram of the aorta as well as a Sudan(III) staining were carried out to visualize the atherosclerotic plaques (FIG. 1). The accumulation factor between normal and atherosclerotic walls was between 3 and 8 depending on the thickness of the plaques (Sudan(III) staining).

    __________________________________________________________________________     #             SEQUENCE LISTING     - (1) GENERAL INFORMATION:     -    (iii) NUMBER OF SEQUENCES: 15     - (2) INFORMATION FOR SEQ ID NO:1:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:1:     #Cys Val Tyr Phe Cys Hiseu Met Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:2:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:2:     #Cys Val Tyr Phe Cys Hisrp Leu Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:3:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:3:     #Cys Val Tyr Tyr Cys Hisyr Lys Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:4:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:4:     #Ala Val Tyr Phe Cys Hiseu Met Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:5:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:5:     #Cys Val Tyr Phe Cys Hisrp Leu Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:6:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:6:     #Cys Leu Asn Phe Cys Hiset Thr Asp Lys Glu     #                 15     -  Gln Asp Val Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:7:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:7:     #Cys Val Tyr Phe Ala Hiseu Met Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:8:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:8:     #Ala Val Tyr Phe Ala Hiseu Met Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:9:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 21 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:9:     #Ala Val Tyr Phe Ala Hisrp Leu Asp Lys Glu     #                 15     -  Leu Asp Ile Ile Trp                  20     - (2) INFORMATION FOR SEQ ID NO:10:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 11 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:10:     #Trpys Val Tyr Phe Cys His Leu Asp Ile Ile     #                 10     - (2) INFORMATION FOR SEQ ID NO:11:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 16 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:11:     #His Leu Asp Ile Ile Trpla Val Tyr Phe Ala     #                 15     - (2) INFORMATION FOR SEQ ID NO:12:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 6 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:12:     -  His Leu Asp Ile Ile Trp       1               5     - (2) INFORMATION FOR SEQ ID NO:13:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 5 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:13:     -  Trp Asp Pro Val Leu       1               5     - (2) INFORMATION FOR SEQ ID NO:14:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 5 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: internal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:14:     -  Glu Ala Ile Leu Trp       1               5     - (2) INFORMATION FOR SEQ ID NO:15:     -      (i) SEQUENCE CHARACTERISTICS:     #acids    (A) LENGTH: 7 amino               (B) TYPE: amino acid               (C) STRANDEDNESS: single               (D) TOPOLOGY: linear     -     (ii) MOLECULE TYPE: peptide     -    (iii) HYPOTHETICAL: NO     -     (iv) ANTI-SENSE: NO     -      (v) FRAGMENT TYPE: N-terminal     -     (vi) ORIGINAL SOURCE:     -            (xi) SEQUENCE DESCRIPT - #ION: SEQ ID NO:15:     -  Cys His Leu Asp Ile Ile Trp       1               5     __________________________________________________________________________ 

We claim:
 1. A compound of the general formula (I)

    B--CO--CR.sup.1 --R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (I)

wherein A,A' are same or different and represent an O, S, or Se chalcogen atom, R¹, R², R³, R⁴, R⁵, and R⁶ are same or different and represent a hydrogen atom or a branched or unbranched C₁ -C₆ alkyl residue, B represents a residue

    --NH--(CR.sup.7 R.sup.8)--(CR.sup.9 R.sup.10).sub.n=1,2 --S--R.sup.11,

wherein R⁷ and R⁸ are same or different and represent a hydrogen atom or an unbranched, branched, cyclic, or polycyclic C₁ -C₆₀ alkyl, alkenyl, polyalkenyl, alkinyl, polyalkinyl, aryl, alkylaryl, or arylakyl residue which may optionally carry additional hydroxy, oxy, oxo, carboxy, aminocarbonyl, alkoxycarbonyl, amino, aldehyde, or alkoxy groups containing up to 20 carbon atoms, and may optionally be interrupted, or replaced, by one or several heteroatoms from the series of O, N, S, P, As, Se, R⁹ and R¹⁰ are same or different and represent a hydrogen atom or a branched or unbranched C₁ -C₆ alkyl residue, R¹¹ represents a hydrogen atom, a sulfur protecting group, or residues R⁷ or R⁸, or with R⁷ and R¹¹, together with --(CR⁸)--(CR⁹ R¹⁰)_(n=1),2 --S--, forming a 4- to 8-membered ring which may optionally carry additional hydroxy, oxo, oxy, or alkoxy groups containing up to 6 carbon atoms, R¹² represents a hydrogen atom or chalcogen protecting group, and their complexes with radioisotopes of Tc or Re.
 2. A compound according to claim 1, characterized in that A and A' represent sulfur atoms and R¹² represents a hydrogen atom or a sulfur protecting group.
 3. A compound according to claim 2, characterized in that R⁷ and R⁸ are different, and R⁸, R⁹, and R¹⁰ each represent a hydrogen atom.
 4. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains the compound according to claim 3, and one or more adjuvants common in galenics.
 5. A method for the production of the compound according to claim 1 characterized in that a first reactant of the general formula (II) is reacted with a second reactant of the general formula (III) according to the following reaction scheme:

    X--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (II)

    +NH.sub.2 --CR.sup.7 R.sup.8 --(CR.sup.9 R.sup.10).sub.n=1,2 --S--R.sup.11(III)

    →B--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (I)

wherein X is an elimination group and R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², A, A', and B have the meanings specified in claim 1and that optionally the compound produced as described above is conjugated to form a conjugate with a substance that accumulates selectively in diseased tissues or tumors with a covalent bond existing between the substance and the conjugate, said bond being amidic if the substance contains carboxy or amino groups including a peptide, a protein, an antibody, or a fragment thereof, ester-like if the substance contains hydroxy groups, including a fatty alcohol, and imidic if the substance contains aldehyde groupsand that the compound and conjugate produced in this way are reacted with technetium -99m or Re in the form of pertechnetate or perrhenate in the presence of a reductant and optionally, an auxiliary ligand.
 6. A compound according to claim 1, characterized in that R⁷ and R⁸ are different, and R⁸, R⁹ and R¹⁰ each represent a hydrogen atom.
 7. A radio pharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains the compound according to claim 6, and one or more adjuvants common in galenics.
 8. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains the compound according to claim 2, and, one or more adjuvants common in galenics.
 9. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains the compound according to claim 1, and, one or more adjuvants common in galenics.
 10. A conjugate containing a compound with a substance that accumulates selectively in diseased tissues, a covalent bond existing between the compound and the substance, said bond being amidic if the substance contains carboxy or amino groups including a peptide, a protein, an antibody, or a fragment thereof, ester-like if the substance contains hydroxy groups including a fatty alcohol, and imidic if the substance contains aldehyde groups, the compound having the general formula (I)

    B--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (I)

wherein A,A' are same or different and represent an O, S, or Se chalcogen atom, R¹, R², R³, R⁴, R⁵, and R⁶ are same or different and represent a hydrogen atom or a branched or unbranched C₁ -C₆ alkyl residue, B represents a residue

    --NH--(CR.sup.7 R.sup.8)--(CR.sup.9 R.sup.10).sub.n=1,2 --S--R.sup.11,

wherein R⁷ and R⁸ are same or different and represent a hydrogen atom or an unbranched, branched, cyclic, or polycyclic C₁ -C₆₀ alkyl, alkenyl, polyalkenyl, alkinyl, polyalkinyl, aryl, alkylaryl, or arylakyl residue which may optionally carry additional hydroxy, oxy, oxo, carboxy, aminocarbonyl, alkoxycarbonyl, amino, aldehyde, or alkoxy groups containing up to 20 carbon atoms, and may optionally be interrupted, or replaced, by one or several heteroatoms from the series of O, N, S, P, As, Se, R⁹ and R¹⁰ are same or different and represent a hydrogen atom or a branched or unbranched C₁ -C₆ alkyl residue, R¹¹ represents a hydrogen atom, a sulfur protecting group, or residues R⁷ or R⁸, or with R⁷ and R¹¹, together with --(CR⁸)--(CR⁹ R¹⁰)_(n=1),2 --S--, forming a 4- to 8-membered ring which may optionally carry additional hydroxy, oxo, oxy, or alkoxy groups containing up to 6 carbon atoms, R¹² represents a hydrogen atom or chalcogen protecting group; and a complex of the conjugate with a radioisotope of Tc or Re.
 11. A conjugate according to claim 10, characterized in that A and A' represent sulfur atoms and R¹² represents a hydrogen atom or a sulfur protecting group.
 12. A conjugate according to claim 11, characterized in that R⁷ and R⁸ are different, and R⁸, R⁹ and R¹⁰ each represent a hydrogen atom.
 13. A conjugate according to claim 12, characterized in that the substance that accumulates in diseased tissue is a peptide including endothelines, a partial endotheline sequence, an endotheline analogue, an endotheline derivative, or an endotheline antagonist.
 14. A conjugate according to claim 13, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof: ##STR2##
 15. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 14, and one or more adjuvants common in galenics.
 16. A method for the production of a conjugate according to claim 10 characterized in that a first reactant of the general formula (II) is reacted with a second reactant of the general formula (III) according to the following reaction scheme:

    X--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (II)

    +NH.sub.2 --CR.sup.7 R.sup.8 --(CR.sup.9 R.sup.10).sub.n=1,2 --S--R.sup.11(III)

    →B--CO--CR.sup.1 R.sup.2 --A--CR.sup.3 R.sup.4 --CR.sup.5 R.sup.6 --A'--R.sup.12                                            (I)

wherein X is an elimination group and R¹, R², R³, R⁴, R⁵, R⁶, R⁷, R⁸, R⁹, R¹⁰, R¹¹, R¹², A, A', and B have the meanings specified in claim 10and that the conjugate produced in this way is optionally reacted with technetium -99m or Re in the form of pertechnetate or perrhenate in the presence of a reductant and optionally, an auxiliary ligand.
 17. A conjugate according to claim 10, characterized in that R⁷ and R⁸ are different, and R⁸, R⁹ and R¹⁰ each represent a hydrogen atom.
 18. A conjugate according to claim 17, characterized in that the substance that accumulates in diseased tissue is a peptide including endothelines, a partial endotheline sequence, an endotheline analogue, an endotheline derivative, or an endotheline antagonist.
 19. A conjugate according to claim 18, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof: ##STR3##20.
 20. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 19, and one or more adjuvants common in galenics.
 21. A conjugate according to claim 10, characterized in that the substance that accumulates in diseased tissue is a peptide including endothelines, a partial endotheline sequence, an endotheline analogue, an endotheline derivative, or an endotheline antagonist.
 22. A conjugate according to claim 21, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof:
 23. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 22, and one or more adjuvants common in galenics.
 24. A conjugate according to claim 10, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof:
 25. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 24, and one or more adjuvants common in galenics.
 26. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 10, and one or more adjuvants common in galenics.
 27. A conjugate according to claim 11, characterized in that the substance that accumulates in diseased tissue is a peptide including endothelines, a partial endotheline sequence, an endotheline analogue, an endotheline derivative, or an endotheline antagonist.
 28. A conjugate according to claim 27, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof:
 29. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 28, and one or more adjuvants common in galenics.
 30. A conjugate according to claim 11, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof:
 31. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 30, and one or more adjuvants common in galenics.
 32. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 11, and one or more adjuvants common in galenics.
 33. A conjugate according to claim 12, characterized in that the peptide comprises one or more of the following sequences or partial sequences thereof:
 34. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 33, and one or more adjuvants common in galenics.
 35. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 12, and one or more adjuvants common in galenics.
 36. A radiopharmaceutical formulation for non-invasive in-vivo visualization of receptors and tissue containing receptors and/or atherosclerotic plaques characterized in that it contains a conjugate according to claim 13, and one or more adjuvants common in galenics. 